The blue sky is more beautiful when you come to Regensburg. It is rumored that the city began to build in the seventh century. It became a castle with combat defense capabilities during the Roman Empire. There are also ruins of ancient Roman walls in the city. Since it is the most complete medieval ancient city in Germany, more than 1,500 buildings in the city are protected by cultural relics. So it was rated a World Heritage Site by the United Nations in 2006!